Heat sealing apparatus for plastic bags

ABSTRACT

An improved plastic bag sealing apparatus comprised of an improved resilient planar heater formed of a heating wire embedded in a resilient silicon rubber material. The heater is shaped to conform to the flat planar surface of a T-bar shaped heating element, and clamped in place with insulators to provide maximum transfer of heat to a heating edge formed by the web portion of the T-bar. In an optional configuration the heater is in the form of a tubular rod seated in a channel in the T-bar directly above the heating edge for transferring maximum heat to the heating edge. The containment of heat and transfer of maximum heat to the T-bar permits a substantial improvement in thermal efficiency and a substantial reduction of power consumption. The heating edge of the T-bar is covered with an easily replaceable heating channel coated with a non-stick, heat resistant material such as polytetraflouroethylene (TEFLON).

SPECIFICATION

This application is a Continuation of application Ser. No. 09/087,752filed May 29, 1998(now U.S. Pat. No. 5,947,019).

BACKGROUND OF THE INVENTION

1. Field of the Invention

This invention relates to a portable heat sealing apparatus for plasticbags and more particularly, relates to an improved more efficient heatsealing apparatus.

2. Background Information

Plastic bags are sealed by heating the perimeter at the opening to thebag. Heat is applied across the opening, under pressure that melts theplastic and "welds" the opening of the plastic bag. There are plasticbag heat sealers that include drawing a vacuuming then sealing theopening by applying heat to melt and weld the opening together. Thesedevices are complicated and expensive, and have jaws that are heated tomelt the plastic bag opening after a vacuum has been drawn in the bag.

There is also a plastic bag heater disclosed and described in U.S.patent application Ser. No. 3,236,174 issued Feb. 22, 1966 to Hutchinsonet al, one of whom is the inventor of the invention disclosed herein.This patent discloses a portable plastic bag sealer that has a sealingedge with controlled heat to seal the plastic bag my applying pressureagainst the opening of the plastic bag with the bag positioned on asurface. The device disclosed is simple in construction and use, and canbe operated by one hand of an operator. It provides superior seals tocomparable portable apparatus that were previously available.

However this device is somewhat thermally inefficient and can have someexposed outer hot surfaces as are typically exposed in the use of hotcloth irons. The heater is in the form of a T-bar that is heated byceramic heating elements on either end. The heating elements mustgenerate a considerable amount of heat energy to heat the entire T-barto attain sufficient high temperature on the heating edge to seal theplastic bag. This results in the entire portable bag sealer becoming hotenough to degrade internal components and thus, shorten the sealersoperating life. In addition, the inefficient heater requires substantialpower to generate sufficient heat to seal a plastic bag.

It is therefore, one object of the present invention to provide animproved plastic bag sealer that provides more efficient heating of thesealing edge.

Yet another object of the present invention is to provide a plastic bagsealer having an improved heater that provides more uniform heat atlower power inputs.

Still another object of the present invention is to provide a plasticbag sealing apparatus, which reduces heat loss by preventing heattransfer to surrounding components and the surrounding atmosphere.

Still another object of the present invention is to provide a plasticbag sealing apparatus that allows small gauge insulation wire to be usedthat is less expensive and lasts longer when used at the reducedtemperatures.

Yet another object of the present invention is to provide an improvedplastic bag sealer having an improved heater that prevents transfer ofheat to external components (e.g., the cover) thereby providing a safersealer.

Yet another object of the present invention is to provide an improvedplastic bag sealing apparatus with an improved heater that preventsinsulating plastic parts from breaking down due to high operatingtemperatures.

Still another object of the present invention is to provide a plasticbag sealer having a silicon rubberized heater with embedded heater wiresthat are clamped in place by insulating plates alone or in conjunctionwith fiberglass insulation.

Still another object of the present invention is to provide a plasticbag sealing apparatus having an improved heater that provides greaterheat transfer to the T-bar edge, and less heat transferred to structuralcomponents.

Yet another object of the present invention is to provide a plastic bagsealing apparatus having an improved flat silicon sheet heater havingembedded heating wires that provide uniform heating over the entirelength and width of the T-bar heater.

Yet another object of the present invention is to provide an improvedplastic bag sealer having an improved heater utilizing thermallyinsulating standoffs that assists in reducing transfer of heat tosurrounding components and external surfaces.

Still another object of the present invention is to provide a plasticbag sealing apparatus having an improved tubular rod heater. Theimproved heater will deliver uniform heat energy concentrated in theimmediate area of the "T-bar" sealing edge. The rod heater designreduces the required input heat and further reduces heat energy loss tosurrounding components and atmosphere.

Still another object of the present invention is to provide an improvedhand-held plastic bag sealer having improved long life elastic foamsupport springs for resiliently supporting an elongate T-shaped heater.

Yet another object of the present invention is to provide an improvedhand-held plastic bag sealer having integrally formed thermallyinsulating standoffs on a heater clamping plate.

BRIEF DESCRIPTION OF THE INVENTION

The purpose of the prevent invention is to provide an improved portableplastic bag sealing apparatus that is more efficient and user friendlythan the model disclosed in the above identified patent.

The plastic bag heat sealing apparatus of the present invention isconstructed of a T-shaped (i.e., T-bar) heating element providing asealing edge that is covered with a replaceable channel having anon-stick, heat resistant and durable plastic coating such aspolytetraflouroethylene (TEFLON). The TEFLON coating on the channel iseffective to prevent the sealing apparatus from sticking to the plasticmaterial. The top of the T-shaped heater is heated by an improved heatercomprised of resilient material having an integral heating wire. Theresilient heater covers the entire surface on the top of the T-barheating element, and is clamped in place with an insulator.

A pair of rails on either side of the heating edge of the T-bar areattached by means of springs that allow the heating edge to pass througha slot formed by the rails to heat a plastic bag positioned on anon-stick surface. The heating assembly is enclosed in a housing whichhas a centrally located handle used to press the heater down whensealing a plastic bag.

A thermostat is provided to vary the temperature of the hot sealing edgeapplied to the plastic bar. The thermostat allows continuous adjustingthe heat intensity according to the thickness of the plastic bags beingsealed. Three different settings are provided. The first setting is forplastic bags or films from one to two mils thick. The second setting isfor medium bags or films three to four mils thick. A third setting forthicker bags having plastic material that is six to ten mils thick isprovided.

The resilient heater is preferably a rectangular shape of soft siliconmaterial having a heating wire encapsulated in the material. The heatingwire is incorporated in the material in a winding path along one side,and winds back along the other side. This provides uniform and evenheating over the entire heater and high heat transfer to the T-barheating element. This results in more uniform heating and lower power toachieve temperatures that provide an efficient seal.

The resilient heating element is also clamped in place, on top of theT-bar heater, and cuts stray heat loss by as much as fifty percent (50%)substantially reducing input power. The reduction in heat transfer tothe surrounding components prevents cracking and damage to thecomponents due to mechanical shock loads during rough handling.

In an optional but preferred embodiment of the invention the rails fromeither side of the heating edge of the T-bar heater are attached byadvanced long life elastic foam support springs constructed of aurethane foam such as that known as PORON manufactured by RogersCorporation of Connecticut. The resilient elastic foam supports do nottake a compression set and therefore has a very long spring life.Further the stress loads on the hand held portable sealer are relativelylight. These foam springs are an improvement over the stainless steelleaf springs, which after many repetitions, can fail. The elastic foamsupport springs because of the light stress loads will have a nearlyinfinite life.

The system is also improved with an integrally formed heater clampingplate and standoffs. The integrally formed clamping plate and standoffsare of a heat resistant thermoplastic resin such as "FORTRON"manufactured by Hoechst Celanese Corporation. This material isparticularly suitable for use in electrical and electronic devices thatrequire high heat resistance. The thermoplastic clamping plate clampsthe heater in place on the T-bar heat sealing element.

In an optional embodiment a rod type heater is used that is lower incost and more directly heats the T-bar sealing edge of the plastic bagsealer. This heater is a cylindrical rod that seats in a channel orgroove in the T-bar heater directly above the heat sealing edge. Thecylindrical rod heater is a heater known as a CALROD heater of GeneralElectric Corporation or an equivalent. The cylindrical rod heater isclamped by a plate having a complimentary groove or channel to securelyhold the heater in place. An insulator is provided between the heaterand clamping plate. Preferably a thermally conductive lubricant orgrease is provided in the T-bar channel to maximize heat transfer to theheat sealing edge.

The above and other novel features of the invention will be more fullyunderstood from the following detailed description and the accompanyingdrawings, in which:

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a isometric view of an improved plastic bag sealing apparatusaccording to the invention.

FIG. 2 is an exploded view of the heat sealing apparatus of FIG. 1.

FIG. 3 is an end view of resilient heater having an embedded heaterwire.

FIG. 4 is a sectional view of an improved resilient heater illustratingthe heating wire configuration.

FIG. 5 illustrates the plastic bag heat sealing apparatus positioned forsealing a plastic bag.

FIG. 6 illustrates the plastic bag heat sealing apparatus sealing aplastic bag.

FIG. 7 is an enlarged view illustrating operation of the plastic bagheat sealer taken at 7 of FIG. 6

FIGS. 8a through 8d illustrate the improved uniform heat transfer anduniform temperature profile of the new resilient silicone heater versusthe old single point isolated ceramic heaters.

FIG. 9 is an exploded view of an optional embodiment of the heat sealingapparatus of FIG. 1.

FIG. 10 is an exploded view illustrating an optional heaterconfiguration for heating the T-bar sealing edge.

FIG. 11 is a sectional view illustrating the optional heaterconfiguration of FIG. 10.

FIG. 12 is an end view similar to FIG. 5 illustrating the optionalheater configuration of the plastic bag sealing apparatus positioned forsealing a plastic bag.

DETAILED DESCRIPTION OF THE INVENTION

A plastic bag sealer is shown in the isometric view of FIG. 1, and issimilar in design to the sealing apparatus disclosed and described inU.S. Pat. No. 3,236,174 issued Feb. 22, 1966 to Hutchinson et al. Theplastic bag sealer 10 has a handle 12 for one-hand operation in sealinga plastic bag 14 lying on a table 16, or other suitable surface whichincludes a pad or mat 18. The temperature of sealer 10 is controlled byknob 20 which controls a thermostat as will be described in greaterdetail hereinafter. The operator grasps plastic bag sealer 10 by handle12, and presses it down firmly against pad 18, on plastic bag 14. Asealing edge heats, melts thereby, seals the opening of plastic bag 14,as will be described in greater detail hereinafter.

The construction of plastic bag sealer 10 is shown in exploded view ofFIG. 2. Plastic bag sealer 10 has a handle 12 as previously described;and a housing or cover 24, covering a heating element 26, heater 28,thermostat 30 and insulators 32 and 34. Plastic bag sealer 10 isconnected to electrical power with cord 36. The construction andoperation of plastic bag sealer 10 substantially reduces powerconsumption and the transfer of heat to surrounding components, allowingsmaller gauge wires 38 and 40 to be used without the heavy insulationheretofore required.

Heating element 26 is in the shape of a T-bar having a flat uppersurface 42, and a vertical centrally located web 44, providing a heatingedge 46, covered by replaceable heating channel 48 having a heatresistant, non-stick coating 49 of TEFLON (polytetraflouroethylene)(FIG. 7). Heating element 26 is heated by rubberized silicon heater 28,as will be described in greater detail hereinafter. Heating channel 48,covering heating edge 46, remains in a normal retracted position (FIG.5) in housing or cover 24, between rails 50 and 52, attached to uppersurface 42 of heating element 26 by leaf springs 54 and 56.

Heater 28 is securely clamped, covering the entire planar surface byMicarta insulator 32, held in place by screws 33. An additionalfiberglass insulator 34 may be clamped between insulator 32 and heater28 if desired. The uniform construction and heating of heater 28 allowstransfer of almost all heat to heating element 26 and heating edge 48with heat loss and transfer to other components being minimized. Housingor cover is insulated from heating element by ligonite standoffs 25 ofimpregnated wood mounted by screws 27 below and screws 29 above. Thiskeeps cover 24 from any contact with heated surfaces.

The construction of heater 28 is shown in greater detail in FIGS. 3 and4. Heating element 28 is comprised of rubber or silicon sheets 58 and 60having a heating wire 62 embedded between the silicon rubberized sheets58 and 60.

The heater 28 is shown in FIG. 4 with upper silicon rubber sheet 58removed for clarity. Heating wire 62 traverses a circuitous path downand along one edge of rectangular silicon rubberized sheet 60 to theopposite end and then back to the other end and is connected to powercord 36 by wires 38 and 40. This arrangement provides uniform heatingover the entire length of heater 28. Slot 64 is provided to fit aroundthermostat 30, which controls the heat applied through knob 20.Thermostat 30 is preferably a short shaft model (MOD HP-84 orequivalent) bi-metal thermostat manufactured by Bimet Corporation ofMorris, N.J.

The application of the device, to seal a plastic bag, is illustrated inFIGS. 5 through 7. Plastic bag 14 is placed on a suitable pad or mat 18,on a flat surface such as a table 16. Plastic bag heat sealer 10 is thenplaced over plastic bag 14, near the opening 15 with rails 50 and 52resting on plastic bag 14 and heating element 26 retracted. With theappropriate amount of heat set by knob 20, plastic bag sealer 10 ispressed downward with handle 12 allowing TEFLON coated heating edge 48to compress bag 14, heating it until it melts and welds the plasticclosed as illustrated in FIG. 7. When handle 12 is released, leafsprings 54 and 56 retract heating edge 48 into housing 24 ready to sealthe next plastic bag. Another plastic bag 14 is then placed on mat 18,and the process is repeated. Each plastic bag can be sealed in just asecond or two.

Thermostat 30 is adjusted continuously by knob 20 to accommodatematerials of different thicknesses. Preferably, three settings areprovided. A first setting is for thin bags or plastic films from one totwo mils thick. A second setting, at a slightly higher temperature, isprovided for bags and films from three to four mils thick. A third andhighest setting is provided for thick bags and films from six to tenmils thick. The thinnest bags will seal in approximately one second,with the thicker bags in the range of three to ten mils thick, will sealin one and one-half to two seconds.

FIGS. 8a through 8d are diagrams that illustrate the improvedperformance from the uniform heat transfer and uniform temperatureprofile of the resilient embedded heater versus the old type heaterusing single point ceramic heaters. FIGS. 8a through 8b diagrammaticallyillustrate the inefficient operation of the isolated ceramic heaters.Isolated ceramic heaters 66, spaced apart on T-bar 68, transfer heat tocoated sealing edge 70 which when pressed down, produce the heatingprofile shown in FIG. 8b. Note, that the temperature gradient variessubstantially (i.e., approximately 50° F.) in the areas directly beneathceramic heaters 66. Thus, considerable heat is needed to assure a sealalong the entire width of the plastic bag.

In contrast, the improved plastic bag sealer provides a more efficienttransfer of heat to seal a plastic bag. Uniform resilient heater 72,securely clamped by insulating clamp 74, uniformly transfers heat toT-bar 76 and coated heating edge 78. The improved portable plastic bagsealer with the uniform resilient heater produces the heating profileshown in FIG. 8d. The resilient heater produces a uniform heat transferand uniform temperature gradient that varies less than about 15° F.beneath the entire sealing edge 78. Since the heat transfer isrelatively uniform over the area being sealed, lower heat power can beused, a more uniform seal is produced and the plastic bag sealer hasless heat transfer to external surfaces making it safer.

A modified preferred embodiment of the plastic bag sealer is shown in anexploded view of FIG. 9 where like parts are indicated by like referencenumbers throughout. The plastic bag sealer has handle 12, as previouslydescribed, housing or cover 24, covering heating element 26, heater 28and thermostat 30 as before. Insulators described previously 32, 34 andstandoffs 35 are replaced by an integrally formed clamping andinsulating plate 35 have an integrally formed standoffs 37, 37'constructed preferably of a thermoplastic resin such as FORTRON, a PPSsynthetic material manufactured by Hoechst Celanese Corporation or anequivalent. This thermoplastic resin clamping plate securely clampsheater 28 on top of heating element 42 and efficiently insulate cover 24and handle 12 from heat. Clamping plate 35 is securely clamped on theupper flat surface of T-bar heating element 42 by screws 39 and attachedto cover 24 by screws 29.

While stainless steel leaf springs 54 and 56 provide an efficientresilient mounting for rails 50 and 52 they are subject to fatigue andsometimes fail after long use. Therefore an improved mounting for rails50 and 52 has been provided as shown in FIG. 9. Leaf springs 54 and 56are replaced with long life resilient elastic foam supports 154 and 156constructed of urethane foam such as PORON manufactured by RogersCorporation of Connecticut, supporting L-shaped rails 150 and 152 byplates 158 and 160. Plate 160 is riveted to rails 150 and 152 whileplates 152 are fastened to each end of heating element 26 by screws 162and insulator 164. Elastic foam support 154 and mounting hardware isthen concealed by insulating covers 168 preferably constructed from anABS (acrylonitrile-butadiene-styrene) thermally insulating plastic.

The plastic bag sealer functions as before. A plastic bag 14 is placedon a pad 18 and heat sealer pressed down on the bag using handle 12.Urethane resilient elastic foam supports 154 and 156 at each end ofrails 150 and 152 act as springs allowing edge 48 to press down and meltthe plastic, welding the plastic edges together. The advantage of theurethane elastic foam support is that it does not take a compressionset. It generally will have a much longer life than the stainless steelleaf springs of the first embodiment. Further since the stress loads arerelatively light they will last almost indefinitely.

While the resilient planar heater of the previously described inventionis more efficient than previous designs to transfer heat to the edge ofthe T-bar flange, a disadvantage is that it transfers substantial heatto the entire T-bar. It is also somewhat expensive to produce becausethe heater is embedded in a flexible planar material. Anotheradvantageous design is the provision of a heater that can transfer moreheat directly to the heating edge of the T-bar heater rather than to theentire T-bar. For that purpose an optional heater configuration has beendesigned.

An optional improved heater design is illustrated in FIGS. 10 through12. In this design the flexible planar heater is replaced by a tubularrod heater 80 known as a CALROD heater of General Electric Corporationor an equivalent. The CALROD heater is a tubular metal design having aheating wire passing through the center which is packed with anelectrically insulating and thermally conductive material. Heater 80 iscomprised of a metal tube 82 having a heating element 84 traversing thelength of the tube with electrical connections 86 and 88 at each end.Electrical connector 86 will connect to cord 36 (FIG. 9) whileelectrical connector 88 will connect to thermostat 30 for temperaturecontrol as before. Generally heating element 84 is embedded in athermally conductive and electrically insulating material to conductheat to metal tube 82.

To maximize transfer of heat from rod heater 80 to heating edge 90 ofT-bar heater 92, a lengthwise groove or channel 94 is provided forreceiving tubular rod heater 80. Clamping plate 96 constructed of a PPS(polyphenylene sulfite) synthetic material, such as FORTRON,manufactured by Hoechst Celanese Corporation that has a complementarygroove or channel 98 to securely clamp rod heater 80 in channel 94 anddirect most heat energy to heating edge 90 of the T-bar as indicated bythe arrow in FIG. 11.

Tubular heater 80 is assembled in T-bar 92 by placing the tubular rod inchannel 94. Preferably a thermally conductive lubricant 102 is firstplaced in channel 94. PPS clamping plate 96 is then securely clamped ontop of tubular heater 80. This construction and configuration serves totransfer maximum amount of heat energy to sealing edge 90 of T-barheater 92. In the configurations shown tubular heater 80 is securelyclamped in arcuate channels or grooves 94 and 98 between clamping plate96 and T-bar heater 92.

The optional configuration for heating described operates in the samemanner previously described, and is shown in FIG. 12. Heating edge 90 iscovered with a replaceable TEFLON coating 48 as before and positionedbetween rails 150 and 152 (FIG. 9) above a plastic bag 14 that is to besealed. Plastic bag 14 is placed on a smooth surface 16 preferablyhaving a heat insulating pad 18. To seal plastic bag 14 a downward forceon handle 12 presses heated edge 90 of T-bar heater 92 against the openend of plastic bag sealed 14 melting the plastic to "weld" it together.

Thus, there has been described a plastic bag sealers, with substantialimprovements over the plastic bag sealer disclosed and described in theU.S. Pat. No. 3,236,174 referred to hereinabove. The plastic bag sealeris provided with a soft silicon heater comprised of a heating wireembedded in the silicon rubber. In an optional embodiment stainlesssteel leaf springs are replaced with urethane elastic foam supports thatact like springs but provide a longer life. The resilient urethane foamsupport acts similar to a spring and have a nearly indefinite lifebecause of the light loads applied to the plastic bag sealer. In anotheroptional embodiment a rod heater is positioned in a arcuate channel inthe T-bar heating element directly above the heating edge to maximumtransfer of heat energy. The tubular rod heater is clamped in acomplementary grooves between the T-bar heater and a thermallyinsulating clamping plate. Heating temperatures and transfer of heatenergy to surrounding components is substantially reduced. A reductionof up to fifty percent (50%) in power consumption to achieve the sameheating temperature is achieved. The sealing edge channel is preferablyTEFLON coated, and is easily replaced on the heating element. Animproved sealing edge and reduction in sticking of the material can beprovided by occasionally wiping the edge of the aluminum sealing channelwith a rag impregnated with silicon oil. The plastic bag sealer quicklyand easily seals plastic bags placed on a back-up mat, providing a goodseal with limited shrinkage.

This invention is not to be limited by the embodiment shown in thedrawings and described in the description which is given by way ofexample and not of limitation, but only in accordance with the scope ofthe appended claims.

What is claimed is:
 1. A heat sealing apparatus for plastic materialscomprising;a T-shaped heating element having an upper planar surface anda flange perpendicular to the planar portion forming a heating edge; atubular rod heater in intimate contact with said upper planar surface ofsaid T-shaped heating element; clamps means firmly clamping said tubularrod heater on top of said T-shaped heating element; said tubular rodheater positioned on said T-shaped heating element to maximize heattransfer to said heating edge; a housing covering said T-shaped heatingelement and said tubular rod heater; a handle on said housing forpressing said heating apparatus downward against a surface; a pair ofrails mounted on either side of said heating edge forming a slot throughwhich said heating edge may pass; biasing means biasing said rail overand beyond the end of said heating edge to maintain said heating edge ina retracted position until ready to use; said biasing means comprisingresilient elastic foam springs supporting said pair of rails; meansconnecting said tubular rod heater to electrical power to heat saidheating element and heating edge; whereby when said heat sealingapparatus is pressed downward on a plastic material placed on a surface,said heating edge passes through said slot between said rails and heatsand seals said plastic material.
 2. The apparatus according to claim 1in which said resilient elastic foam springs are constructed ofpermanent set heat resistant urethane foam.
 3. The apparatus accordingto claim 2 including a replaceable heating channel mounted over andcovering said heating edge of said T-shaped heating element.
 4. Theapparatus according to claim 3 wherein said replaceable heating channelis coated with a heat resistant non-stick coating.
 5. The apparatusaccording to claim 4 in which said heat resistant, non-stick coating ispolytetraflouroethylene.
 6. The apparatus according to claim 5 in whichsaid clamping means comprises an insulator having the same shape as saidupper planar surface securely fastened to said T-shaped heating elementon top of said heater.
 7. The apparatus according to claim 6 in whichsaid clamping means comprises a clamping plate of polyphenylene sulfide.8. The apparatus according to claim 7 including attaching means forattaching said heating element to said housing with polyphenylenesulfide standoffs to minimize heat transfer to said housing.
 9. Theapparatus according to claim 8 in which said standoffs are integrallyformed on said clamping plate.
 10. The apparatus according to claim 1including a replaceable heating channel mounted over and covering saidheating edge of said T-shaped heating element.
 11. The apparatusaccording to claim 10 wherein said replaceable heating channel is coatedwith a heat resistant non-stick coating.
 12. The apparatus according toclaim 11 in which said heat resistant, non-stick coating ispolytetraflouroethylene.
 13. The apparatus according to claim 1 in whichsaid clamping means comprises an insulator having the same shape as saidupper planar surface securely fastened to said T-shaped heating elementon top of said heater.
 14. The apparatus according to claim 13 in whichsaid clamping means comprises a clamping plate of polyphenylene sulfide.15. The apparatus according to claim 14 including attaching means forattaching said heating element to said housing with polyphenylenesulfide standoffs to minimize heat transfer to said housing.
 16. Theapparatus according to claim 15 in which said standoffs are integrallyformed on said clamping plate.